tech tip #1 - federal corporation you end up doing is making your boiler and piping system a...

282 www.federalcorp.com

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TECH TIP #1Which Boiler is Right For Me?

OKLAHOMA CITY • (405) 239-7301 TULSA • (918) 249-1918 (800) 289-3331 • FAX: (405) 232-5438 (800) 955-1918 • FAX: (918) 249-9014 283

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TECH TIP #1 (Cont.)


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TECH TIP #1 (Cont.)


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TECH TIP #1 (Cont.)

For more information concerning boilers and boiler applications, please contact a sales representative at Federal.


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TECH TIP #2BOILER TYPE AFFECTS SCALING & EFFICIENCY


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TECH TIP #2 (Cont.)BOILER TYPE AFFECTS SCALING & EFFICIENCY


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BOILER WATER TREATMENT

Here are the three most important rules of taking care of boilers, chillers, and heat exchangers… in fact, any equipment:

1. Water treatment2. Consistent water treatment3. Monitored consistent water treatment

Get the picture? Nothing is more important to the efficiency, longevity and maintainability of your hydronic system than water treatment. Show us a system that is not treated and we know you will be spending a lot more on your energy bills and replacing the equipment long before it’s useful life should be over.

Did you realize that scale on a boiler tube the thickness of an eggshell will cost the owner about 10% more in fuel? But the thicker the scale becomes the quicker you lose efficiency, the loss is not linear. At a mere .20 of an inch your energy efficiency drops off 50%. In other words, scale about a ¼” thick will force your boiler to burn 50% more fuel to provide the same heating capacity as when it was brand new and clean. QUICK…call the water treatment experts!!!!!! It will cost you big bucks if you don’t treat your system.

In addition to the heat transfer surfaces, untreated systems will experience premature failures with pump seals, valve packing and piping corrosion. We can not stress it strongly enough, water treatment is an investment not an expense.

ADVANCED TECHTIPS…Please contact us for further information on how to protect your investment and reduce your energy bills.

TECH TIP #4


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IS A DEAERATOR REALLY NECESSARY?

The following is an excerpt from an article that first appeared in an Industrial News-letter sometime ago. The full title for the article was “Is a Deaerator Really Necessary –or- How to Return Your Piping System to the Boiler”.

From time to time we hear the question, “Why do we need a deaerator, we’ve been operating for twenty years without one?” Or, How can you justify the extra expense of a deaerator over a standard inexpensive boiler feed system?”

It is difficult to argue with this type of rea-soning because a deaerator is a long-term investment with variable pay off. But pay off there is!

Now we are going to tell you something that may shock you. Under the proper conditions, it is theoretically possible for one pound of oxygen to combine with four pounds of iron (iron oxide…Rust!) This is not to say it is a promised fact but merely a probability. Along with Carbon Dioxide in the steam, the chances become four (4) times greater of achieving this theoretical balance. This means it is possible for the oxygen in 16 GPM of water to remove, oxidize and/or dissolve nearly 50 pounds of iron per week. Where does the iron pipe go? It comes back to the return line, to the feed system, pumped into the boiler and then blown down to the sewer. There goes your piping system, boiler, expensive heat exchangers and other system components…Down the sewer!

If you, or the contractor, or the customer, or the engineer, think you can short cut an over-budgeted job by ignoring the laws of nature, you are fooling yourselves…but don’t try to fool Mother Nature…She will get you eventually!

What you end up doing is making your boiler and piping system a deaerator because the oxygen and carbon dioxide are going to react someplace…the laws of nature demand it.

YOU ARE NOT DOING ANYONE A FAVOR WHEN YOU LEAVE OUT THE DEAERATOR…SPECIFY A QUALITY DEAERATION SYSTEM AND SLEEP AT NIGHT.

ADVANCED TECHTIPS…We have several articles that go into deaerator selection, sizing and operation in great detail. Contact our office for further information.

TECH TIP #5


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TECH TIP #6ENERGY SAVINGS WITH STACK ECONOMIZERS

Courtesy Heatmizer, inc.-- www.heatmizer.com

HEATING PROCESS OR DOMESTIC HOT WATER

The most effective use of recovered heat from natural gas combustion is in heating hot water for process or domestic use. The reason is that the lower the entering water temperature becomes, the higher will be the temperature difference from the entering flue gas temperature, and the greater will be the heat extracted. Water temperatures below about 120ºF will usually cause condensation of the water vapor formed by the combustion of hydrogen in the natural gas. The HEATMIZER is designed with corrosion resistant materials and a condensate separation and drainage system to remove con-densate. Collected condensate has given up its latent heat to the water circulated through the HEAT-MIZER, increasing the recovered heat.

Hospitals usually have standby #2 oil to fire in emergencies. We recommend bypassing the products of combustion around the surfaces of the heat exchanger in such cases of limited oil firing due to pos-sible corrosion from the sulphur content of the oil. We offer a built-in bypass as a standard equipment option.

The hot water circulation rate is usually sized at 7 GPM per 100 Boiler HP and should be installed to pull water off the bottom of the tank and also from the cold water supply (CWS) for the coolest enter-ing water to produce maximum HEATMIZER savings.

An aquastat is located near the top of the storage tank to limit the tank temperature. If the heat recov-ered exceeds the heat required by the tank, the HEATMIZER is switched to bypass the fluegas until the tank is cooled.

Note the flue gas recirculation (FGR) duct in the illustration. This duct connects from a flange on the cold side of the HEATMIZER to the burner inlet air louver chamber on a low NOx burner. As low NOx is obtained by lowering combustion flame temperatures, the cooler FGR will reduce the NOx by several PPM.

HEATING BOILER FEEDWATER

The most common use of recovered heat from flue gas is in heating boiler feedwater. This is mainly because the heat sink is the boiler and the flue gas flow from the boiler is proportional to the steam generated and in turn to the feedwater flow.


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The temperature of the tank will vary depending on the amounts of cold water makeup to the boiler and the condensate return temperature from the system. For example, with 20% cold water makeup and 180ºF condensate return, one would expect an average tank temperature of 156ºF (without any additional steam or waste heat added). The colder the tank temperature, the greater the heat recov-ery, as this creates a greater difference between the water to the HEATMIZER and the entering flue gas temperature, enabling a further lowering of the exit gas temperature with consequently greater savings.

The HEATMIZER requires a continuous water flow through the unit whenever the burner is operat-ing to prevent boiling in the heat exchanger as well as to efficiently utilize the additional investment. This involves operating the feedwater pump whenever the burner operates. This also requires proper sizing of the feedwater pump to avoid inefficient operation at low loads. For example, with on-off FW pump operation, it is normal to size the pump at 2 times the boiler evaporation rate so it can catch up quickly on a call for water. On a continuous flow HEATMIZER installation, this practice would result in an oversized pump, particularly at low firing rates. Most FW pumps must have a minimum flow of approximately 10% (of max flow) for proper cooling. Good practice is to use a back pressure regulating valve to bypass water back to the tank when the boiler feed water valve is closed, thus assuring the required minimum cooling flow at pump and HEATMIZER.

A fluegas bypass option is normally provided as standard with the HEATMIZER. A high limit aquastat, mounted at the tank that receives flow from the backpressure regulator, will automatically switch the HEATMIZER to bypass fluegas until the tank temperature drops to normal.

Fluegas condensation will occur when HEATMIZER entering water temperatures are 120ºF or lower. Condensate lines should be terminated slightly above the drain so that flow may be easily observed. The condensate from the combustion of hydrogen in natural gas is slightly acidic (Ph about 4 or 5). This will not damage the drain. Boiler room drains also usually receive boiler blow down water, which is alkaline and which tends to neutralize the condensate.

Good operation of the HEATMIZER is based on the premise of continuous operation and steady state conditions. To obtain these conditions, it is necessary to have modulating control of firing rates and water levels on both the boiler and the DA. This type of control is common for larger boilers, especially the wa-tertube types which, having low water volumes, require continuous feedwater flows. Modulating controls are not as common on fire tube boilers, even larger ones. Higher turndown burners help reduce the low fire rate, which aids in keeping the burners “on” and helps reduce the “on-off” cycle with its accompanying high loss of efficiency during burner pre- and post-purge.


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TECH TIP #7CONTINUOUS TOP BLOWDOWN HEAT RECOVERY

Courtesy Madden Mfg.-- www.maddenmfg.com

How Does it Work?

Hot, High pressure continuous blowdown water drained from the boiler, contains valuable heat energy. The continuous blowdown process helps control boiler water quality and operating efficiency by removing suspended and dissolved solids from the water in the boiler drum.

Recovery of up to 50% of the BTU’s available may be accomplished by generating low pressure flash stream in a flash tank. This supply of stream can be used in boiler D/A tank or other low pressure steam applications. As the flash steam is generated, the blowdown condensate that remains is used to preheat the boiler feed water using a low pressure liquid heat exchanger. For smaller, lower pres-sure blowdown requirements, the HX Series heat recovery system utilize a higher pressure liquid to liquid heat exchanger without a flash tank to do the heat recovery job. Contact a Federal sales rep-resentative will recommend the model you need to maximize your fuel savings potential.

kRecover 90% of the heat energy in continuous top blowdown that would be lost down the drain. kReduce temperature of blowdown discharge to drain to meet statute limits. kFast investment payback from fuel, cooling water and makeup water savings, Mad-den systems usually pay for themselves in less than 12 months. kDurable, time proven designs, built to take the punishment of continuous, 24 hour a day service for years.


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TECH TIP #8VFD APPLICATIONS IN THE BOILER ROOM

Just as our industry is discovering electrical power savings through the application of variable frequency drives controlling motors on air handlers, circulating pumps, cooling tower fans and many others pieces of equipment, the boiler room is no exception. Two motors to better control are the fan motor on the burner and the boiler feed pump (on a steam boiler). Although small motors can be controlled by drives, the larger the motor, the more potential for savings. Steam boilers larger than 200 Boiler HP can be considered candidates. Special boiler control systems are necessary to generate signals which can be used by VFDs. (See Tech Tip #9) This is most easily added if a new boiler is being ordered or an existing boiler is being re-controlled.

Electrical savings from 5-50% can be expected! Savings depend on the application, but the more the boiler runs at part-load, the more the savings. If the combustion air and feed water can be controlled with a VFD rather than primarily a fan damper or water valve, there are savings.

Following are two examples of calculations of savings on larger boilers. TechStuff software (on the Federal website) is used in these examples. Example 1 shows the calculations on a 30 HP blower motor on a burner. Example 2 shows savings on a continuously run boiler feed pump. Let a sales professional at Federal help you survey your boiler room for possible savings.


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TECH TIP #9METERED FUEL/AIR RATIO CONTROL PLUS O2 TRIM

by David Farthingfrom Federal Corp. Technical Library--www.federalcorp.com

Today's economic and environmental de-mands dictate that we get the greatest practical efficiencies from our plant. To do this, we must have a basic understanding of what those efficiencies are and how to implement them.

NEW TECHNOLOGY IMPROVES OVERALL COMBUSTION EFFICIENCY AND BURNER STABILITY WHEN LOADS AND DEMANDS

ARE VARIABLE.

Advanced automatic systems for combus-tion control are excellent methods for im-proving systems and process automation success. New technology available today helps improve overall combustion effi-ciency and burner stability when load and demands are variable. The most sophisti-cated systems can eliminate the need for operator input during load changes while maintaining safe and reliable fuel/air ra-tios.

This discussion describes several systems, from the simplest to the most elegant, and focuses on the features, benefits and appli-cations of several system applied to single-burner packaged boiler.

A Look at Combustion Strategies

Here are some control strategies to con-sider for improving burner efficiency. The right strategy depends on boiler loads, demands-and economics.

Fixed Position Parallel Controls. The sim-plest form of combustion control for power burners is the fixed position parallel control (FPC) (Figure 1) also known a direct or jack-shaft control. This strategy incorporates a single positioning motor, which drives both the fuel and air positioning devices via an interconnected single mechanical link, the jack-shaft.

The simplicity of the FPC control strategy makes it a very economical choice for small burners with modest firing rate changes. However, because fuel and air are fixed, the fuel/air ratio is also fixed. The burner cannot compensate for environmental changes such as combustion air tempera-ture or fuel pressure. Additionally, the FPC strategy lacks feedback to the control ele-ment, which can cause fuel to cross over the airflow and cause a fuel-rich furnace or other burner efficiency losses.

To help prevent a fuel-rich furnace, FPC sys-tems are set to allow 4% to 8% excess oxy-gen to the furnace. In practice, the excess oxygen is normally set at 6% to 7%, allow-ing for seasonal air temperature changes.

Parallel Positioning Control Systems. These systems function similarly to FPC systems, except that fuel and air end-devic-es are separated and driven by individual positioners. Modern electronic parallel po-sitioning control (PPC) incorporates end-device positioning signals to ensure accu-

rate placement of fuel and air positioners for specific firing rates. These signals make PPC system much improved over FPC sys-tems.

The new systems are gaining acceptance over FPC systems because they offer an economical means to improve overall combustion efficiency. PPC systems are suitable for 100 to 900 boiler horsepower (Bhp) boilers that operate with relatively stable loads. Larger systems are also be-coming more prevalent.

PPC systems can hold excess oxygen levels to within 3% to 4% in many applications, but because they lack true process vari-able feedback in the fuel/air systems, they should be used cautiously in applications with extremely fast load swings. Like FPC systems, PPC systems cannot compensate for changes in fuel or combustion air char-acteristics.

Series Metered Control Systems. Boilers larger than 750 Bhp commonly incorpo-rate series metered control (SMC) systems, where load changes are neither large nor frequent. In this application, both fuel and air are metered. The boiler master control-ler regulates combustion airflow with a set point. The airflow controller cascades the airflow signal to the fuel controller as its remote set point. A ratio algorithm signal sent to the fuel controller adjusts the fuel/air ratio.

Metered Parallel Positioning Control Sys-tems. Boilers operating at 1,000 Bhp or higher may incorporate metered parallel positioning control (MPPC) systems. These operate the fuel and air control loops in parallel from a single setpoint generated by the boiler master controller. A combustion air set point ratio establishes the fuel/air proportions.

This fuel/air customization feature means excess oxygen in the exhaust gases may be reduced to 3% to 4%. To maintain an air-rich furnace on transition, MPPC systems are normally set with additional excess air to compensate for fuel flow during setpoint excursions. In practice, the excess air is set at 4.5% to 5% to compensate for barometric changes in air density. During steady-state operation, this can be adjusted to 2.5% to 3% using an oxygen trim system.

Cross-limited Parallel Metered Control Systems. This strategy improves on MPPC

Figure 1. Fixed position parallel jackshaft combustion system with fuel/air ratio estab-lished through fixed mechanical linkages.


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TECH TIP #9 (Cont.)METERED FUEL/AIR RATIO CONTROL PLUS O2 TRIM

by interlocking fuel/air ratio control to pre-vent a fuel-rich furnace. The cross-limited control (CLC), or lead-lag control (Figure 2), is dynamic and easily adjusts to different response times of the fuel and air end de-vices. This flexibility allows its use in sys-tems with sudden and large load swings and provides precise combustion control at steady-state operation.

CLC systems easily maintain excess oxygen levels at 3% to 4% in gas burners and 2.5% to 3% in #2 oil systems. Additionally, the cross-limiting feature prevents fuel from overshooting airflow.

Because of its capability for close tolerance control, CLC systems are suited for all sizes of boilers that can support the systems installation cost. Additionally, the CLC sys-tem can be readily adapted to oxygen trim control and is suitable for most low-NOx burner applications.

Selecting a Strategy

The economic balance between fuel cost, safely, boiler load, and control system cost will eventually determine which of these systems best suits your process.

Calculated savings on a sample 600 HP steam boiler comparing manual Jack-Shaft Control to Cross Limited Control with O2 trim.

Figure 2. Cross limiting, or lead-lag fuel/air ratio control, is the most dynamic of all combustion control strategies.


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TECH TIP #10 BOILER FEED PUMP SIZING AND SELECTION

Courtesy Industrial Steam--www.industrialsteam.com


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TECH TIP #10 (Cont.)


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TECH TIP #11

STEAM BOILER RATINGS & FEED PUMP CAPACITY REQUIRED (ON-OFF OPERATION)ON-OFF pump operation is used on smaller boilers. Modulating feed water should normally be considered on boilers larger than 100 boiler HP. (See Tech Tip 10)


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BOILER CODE EXPLANATIONS

Many different codes are adhered to in Oklahoma; here’s a listing of the main approval bodies that we run across.

Oklahoma State Boiler Code: Obviously the number one agency for approving a new boiler installation in the state of Oklahoma. We find that the inspectors are a very knowledgeable and conscientious bunch. Anytime there is an interpretation to be made they should be consulted. The Oklahoma City office telephone number for the Chief Boiler Inspector is (405) 528-1500, extension 242, or the statewide number is 1-888-269-5353, extension 242.

Controls and Safety Devices (CSD-1): CSD-1 code is a term that you will hear in Oklahoma quite a bit. The Ok State Boiler Code adopted this back in July 1994. CSD-1 is an amendment to the ASME code that gives a level of safety that adopts most of the UL code and some of the IRI and FM requirements. CSD-1 is a state requirement on any combustion equipment above 400,000 btuh input.

GE Capitol (formerly Industrial Risk Insurance-IRI): GE Capitol has long been recognized as a level of safety above the standards that UL rec-ognize. On any piece of gas fired equipment above 2,500,000 btuh input it is prudent to strongly consider requiring the GE Capitol approval.

Factory Mutual Insurance (FM): FM is another insurance industry standard that will require additional safety controls. Again, on the larger boil-ers, if you are serious about safety insist on one of the agency approvals such as FM.

Underwriter’s Laboratories (UL): UL has been one of the most basic approval bodies in North America for many years. Insist that your equip-ment carry the UL label.

American Society of Mechanical Engineers (ASME): ASME has set up a code that should be followed in the construction of the boiler. No manufacturer would consider building a boiler without ASME approval.

National Board (NB): NB has the unenviable job of keeping track of all the pressure vessels built. The NB registers all manufactured boilers and pressure vessels, trains inspectors and provides accident investigation services.

ADVANCED TECHTIPS…The above listing is by no means exhaustive or meant to cover all the nuances of each code. Please contact us for a thorough explanation of the code requirements as needed. Tech Tip #13 is published by Gordon-Piatt and details many of the different requirements of each of the typical gas controls used in conjunction with the above agencies.

TECH TIP #12


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GAS TRAIN BASICS

GAS TRAIN COMPONENTS..To Vent or Not To Vent Do I need to vent the gas pressure switches? The gas regulator? What about my V88 diaphragm gas valve? What about the normally open vent valve? Can I combine these vents so I don’t have to run several lines?

A. According to UL 795, the “normally open” vent valve line must be run to a safe location outside by itself, no other vent line can be combined with it. (See below for an alternative to using normally open vent valves.)

B. According to UL 795, the vent off of a gas regulator must be run to a safe location outside by itself, no other vent line can be combined with it.

C. In order to use a vent limiter on a gas regulator, the following guidelines are suggested:1. Maximum inlet pressure to regulator 5#.2. Maximum regulator size is 1”.3. Regulator must be mounted in upright, horizontal position. 4. Can only be used if boiler/appliance is within 6’ of regulator.5. Vent limiter must be manufactured by the regulator mfg.

D Vent outlets from gas pressure switches & diaphragm gas valves (V88) can be “ganged together” into a single vent line, provided the cross-sectional area is a least the size of the largest vent opening plus 50% of the area of all additional vent lines. See the following photo for details.

NOTICE: Always terminate vents away from air intakes or sources of ignition. Be sure that moisture and insects cannot enter the pipe(s) as well. Always utilize a drip leg to keep incidental moisture from traveling back down vent tubing and damaging the diaphragm.

TECH TIP #13

How to Avoid the Need for a NORMALLY OPEN VENT VALVE Honeywell (and possibly others) now manufacture combustion flame safeguard control systems called VPS (Valve Proving Systems) which prove the “double block” valves. We recommend this system instead of the “double block and bleed” system which has traditionally been used. This new system eliminated possible fuel leaks to the atmosphere, saves expense in installation and also increases safety.


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GAS TRAINS--WHAT DO THE CODES REQUIRE?TECH TIP #13 (Cont.)


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TECH TIP #13 (Cont.)GAS SYSTEM SCHEMATICS

UL, FM & CSD-1 (which requires a plugged leak test cock downstream of each safety gas valve) Systems


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TECH TIP #14WHAT CODES APPLY TO RELIEF VALVES? WHAT DO ALL THOSE

FUNNY LETTERS MEAN?


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BOTTOM BLOWDOWN VALVE OPERATION FOR STEAM BOILERS

Everlasting Valve Company, the premier boiler bottom blowdown valve manufacturer, recommends the following operating procedure when performing a bottom blowdown on your boiler.

1. Before cutting boiler into line, blowdown to reduce the alkalinity. This prevents carryover. Test the water and give blowdowns until the water is just right. Consult with your water treatment specialist to determine frequency and duration of blowdowns.

2. Blow out sediment, mud or scale while boiler is steaming. Important: make certain blowdown valves are closed on idle boilers or scalding water will blow into

them.

3. Blow down when boiler has a low load. Sediment settles more under these conditions. Watch gauge glass; don’t leave an open valve.

4. Be careful when blowing down boilers. First, open quick-opening valve slowly; then open slow-opening valve slow enough to prevent shock, but fast enough so valve seat won’t wire draw. To stop blowing down, close slow-opening valve quickly; then close fast-opening valve.

5. Never jam a blowdown valve if it won’t close. Open a few turns fast to clear, then close again slowly. Try this several times to dislodge any scale or sediment. Jamming on scale will wire-draw or score the seats and disc of valve.

6. For cleaning, inspection or repairs, empty cold boiler through blowdown line. Never empty until the boiler is quite cool, or boiler seams and joints may warp and cause leakage.

ADVANCED TECHTIPS…..The next page is reprinted by permission of Everlasting Valve Company. It details the service and selection of blowdown valves as detailed by ASME/ANSI. For further information contact our office or consult the latest ASME Boiler & Pressure Vessel Code, Section I.

TECH TIP #15


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Boiler Blow Down Back to Main Page

Back to Main Page Selector Guide (pg 1) Selector Guide (pg 2) Selector Guide (pg 3) Selector Guide (pg 4)

Page 1 of 1Everlasting Valve Co. - Boiler Blow Down

8/25/2008http://www.everlastingvalveusa.com/boilerblowdown2.htm



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TECH TIP #16BOILER/BURNER SURVEY FORM FOR CSD-1


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BOILER/BURNER SURVEY FORM FOR CSD-1


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TECH TIP #16 (Cont.)BOILER/BURNER SURVEY FORM FOR CSD-1


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TECH TIP #17

Lloyd L. FieldsCOMMISSIONER Chief Boiler Inspector

Tom Monroe

MANUFACTURER'S/INSTALLING CONTRACTOR'S REPORTFOR MEETING THE REQUIREMENTS FOR ASME CSD-1 (CG500)

UNIT MANUFACTURERName

Address ZipCity/State

Telephone Fax

UNIT IDENTIFICATION (Boiler)Manufacturer's Model # Year BuiltASME # Nat. Bd. #

AGA #UL #OK #

STEAM HOT WATERMax. W.P. psigMin. Safety Valve Cap. PPH Max. temp. deg. F

psigMax. W.P.

Min. Safety Relief Valve Cap.PPH or Btu

BOILER UNIT DESCRIPTION (TYPE)If Modular (No. of Modules)

BOILER UNIT CAPACITY (OUTPUT)

Burner - Manufacturer ModelSerialUL or AGA #

FUELS (as shipped)

Customer NameINSTALLATION LOCATION (if known)

AddressCity State Zip

FaxTelephone

OperationalTest

Performed,DateModel #ManufacturerControl/Device

OPERATIONAL CONTROLSLow-Water Fuel Cutoff CW-120(a), CW-140Forced Circulation CW-210(a)Steam Pressure CW-310(b)Water Temperature CW-410(b)

4001 N. LINCOLN BLVD, OKLAHOMA CITY, OKLAHOMA 73105-5212 - PHONE (405)528-1500 FAX (405) 525-0252

Print Form

By state law, the contractor must submit this form to the State Boiler Inspection Office and re-quest a boiler inspection for every boiler installation. This form is also available on-line by going to the Oklahoma Department of Labor Safety Standards Division page on the State of Oklahoma web site www.ok.gov/odol


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High Water Temperature Limit CW-400(c)

High-Steam Pressure Limit CW-310(c)

Forced Circulation CW-210(b)

Low-Water Fuel Cutoff CW-120(a), CW-120(b), CW-130, CW-140

SAFETY CONTROLS

OperationalTest

Performed,DateModel #ManufacturerControl/Device

Fuel Safety Shutoff Valve, 1 CF-180Fuel Safety Shutoff Valve, 2 CF-180Pilot Safety Shutoff Valve, 1 CF-180(c)Atomizing Medium Switch CF-450(b)Combustion Air Switch CF-220High Gas Pressure CF-162

Low Oil Pressure CF-450(a)High Oil Temperature CF-450(c)Low Oil Temperature CF-450(d)Purge Air Flow CF-210Flame Safeguard (primary) CF-310. CF-320Flame Detector CF-310, CF-320LOW FIRE STARTLow Fire Start Switch CF-610

Low Gas Pressure CF-162

SAFETY OR SAFETY RELIEF VALVE(S) CW-510, CW-520

OPERATION TEST PERFORMED, DATE

Manufacturer

ModelSize

Capacity PPH/Btu/hr

Date

Representing Equipment Manufacturer, Name

Signature

Date

Signature

Representing Installing Contractor, Name

License #Revised 11-9-07


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TECH TIP #18WATER LEVEL CONTROLS FOR STEAM BOILERS

Steam Boilers

They’ve been with us for over two hundred years, and most of the time they’re so reliable most folks don’t give them much thought. They sit in buildings all over the world, transferring heat from fuel to water, allowing us to warm our buildings or complete our processes.

Steam boilers are simple, efficient and reliable. No machine does a better job of moving BTUs from one place to another. We’ve used them for space heating since before the United States Civil War in 1861.

Even before the Civil War, we used steam boilers for industrial processes. Today we use them to run factories, press clothes, wash dishes, pasteurize milk, sterilize medical equipment, and to heat entire cities! Their capabilities seem endless.

But despite its simplicity, any steam boiler can run into trouble if its control system doesn’t act properly. If the energy you put into the boiler exceeds what the boiler can absorb, the boiler can rupture. So you must always be on guard.

A simple safety relief valve of the right capacity and relief-pres-sure setting protects the boiler from over pressure. But over pressure isn’t the only thing that can threaten a steam boiler. There are also the dangers of dry firing.

Should the internal water level drop too low, the boiler can burn out. So here too, you must always be on guard. You see, a steam boiler needs its water to move the heat away from its metal surfaces. Without the right internal level of water, heat quickly accumulates. Too much heat creates a very dangerous operating condition.


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Boiler manufacturers have always set up minimum safe water level requirements for their equipment. Our controls help enforce those requirements in two ways:

• By maintaining a minimum safe water level in the boiler.• By signaling the burner to stop should the water level drop below that point.

In this brief Systems Guide we will explain how we do these two very important jobs.

What’s a “Normal” Water Level?

The proper steam boiler water level varies from manufacturer to manufacturer, but generally we can say that it’s “normal” to start by manually filling the boiler to the two-thirds-full point on the gauge glass. As the boiler operates, the water will quickly turn to steam and head out toward the system.

Steaming takes place at a constant rate of about one-half gpm per 240,000 BTU/HR (D.O.E. heating capacity rating). This is a law of physics, so it doesn’t vary from manufacturer to manufacturer. If you’re working with a boiler with a rating of say 1,000,000 BTU/HR, you can be assured the water is turning to steam and leaving that boiler at the rate of about two gpm. And it’s leaving at speeds measured in miles per hour (sometimes exceeding 60 mph!). So it’s very important for your near- boiler piping to be correct. If it’s not, the fast moving steam will pull water out of the boiler and create problems for you in the system and the boiler.

As the water (in the form of steam) heads out toward the system, the water level in the boiler will, of course, drop. How far it drops depends a lot on the size and condition of your piping system. You see, ideally, the water should begin to return to the boiler before the boiler’s internal water line drops to a critical point. That’s the point at which the low water cut-off will cut power to the burner, or an automatic water feeder will open.

Because the water is in the system piping and radiating during operation, the “normal” water level becomes a point that’s somewhere in the lower-third of the gauge glass.

Remember that you’re working with a range of operation here, not a fixed point. If the water were to stay at the top of the gauge glass all the while the burner was firing, you probably wouldn’t be making steam! So don’t get too caught up with the word “normal” because the only thing that’s normal is that the water level will rise and fall.

Boiler manufacturers, as we said before, do establish a mini-mum safe water level for their boilers, however. That point


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is usually just out of sight of the bottom of the gauge glass. Should the water level drop to this point, the boiler may be in danger of overheating. We have to find a way to protect the boiler from itself.

All leading authorities and insurance companies recognize this need. The ASME Code for Low Pressure Heating Boil-ers, for instance, specifies, “Each automatically fired steam or vapor steam boiler shall be equipped with an automatic low water fuel cut-off.” The device the code refers to is what most people in the field commonly call a “low water cut-off.” Its job is to stop the burner and protect the boiler.

What Causes a Low Water Condition?

Because it’s an open system, some evaporative water loss is normal for a steam system. How much depends on the size and condition of the system. If you’re losing too much water, however, it’s time to begin troubleshooting. There are many places to look

Here are a few good places to start:

•The air vents are dirty, not seating properly, and passing steam to the atmosphere.

• Someone left the boiler blowdown valve partially open.

• Someone, for whatever reason, has been drawing hot water from the boiler.

• The relief valve has discharged.

• The condensate pump isn’t working as it should.- The float may have come loose.- The condensate may be too hot to pump. (Check those steam traps!)

• Improper near-boiler piping may be throwing water up into the system, or causing the waterline to tilt during operation.

• The wet returns may be leaking. (Always suspect any buried pipe).

• A check valve may be stuck closed or partially closed.

• The boiler may be foaming and priming.- Check the pH of the water. It should be between 7


and 9.- Check the condition of the water. Dirty water will prime and foam.- Check the burner’s firing rate. Over-firing can cause priming.

• The pipes may not be properly pitched.

• The automatic feeder may not be working properly. - Its chamber may be filled with sediment. - Its feed line may be clogged.

• All of the condensate may not be returning from the system (a common problem with process applications).

• The boiler metal may be corroded and leaking at the water line.

- Flood the boiler to its header to check for leaks.

Good troubleshooters take the time to look over the entire system before deciding what’s wrong. Take the time to do it right, and you’ll be the person with the answers

Watching the Water Level

The best way to prevent overheating damage to a boiler is to stop the burner if the water level falls too low. This is the low water cut-off’s job. There are several types of low water


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cut-offs you can use. Let’s look at them.

Float Operated Low Water Cut-Offs

Float operated low water cut-offs have been around since the 1920s and have earned a reputation worldwide for reliability. Usually you’ll mount this type of low water cut-off directly in the boiler’s gauge glass tappings. We make “quick hook-up” fittings for these units to simplify installation.

The water level in the low water cut-off’s chamber will mimic the water level in the boiler. As the water level drops in the boiler during steaming, the level in the chamber, and the cut-off’s float drops with it. Should the float drop to the boiler’s critical low water cut-off point, the float will trip an electrical switch that’s wired in series with the burner. The burner instantly stops firing. It will stay off until the water level rises to a safe operating point.

This happens when the condensate returns from the system or when an automatic water feeder or a boiler attendant adds water to the boiler. When the level reaches a safe position, the low water cut-off will make its electrical connection and the burner will restart.

When a steam system is well balanced, the low water cut-off’s job is to stand by and wait. The situation we just described suggests that there’s something out of balance in that system. We’ll look at this again in a few minutes.

Probe and Float Type Built-In Low Water Cut-Offs

There are some jacketed boilers that don’t easily accept quick hook-up fittings. These boilers will often have a tapping for a built-in low water cut-off. These built-in units do the same thing as the external units we just looked at, but instead of being in a chamber, the “built-ins” are right inside the boiler where they can sense the water level directly.

We make two types of built-in low water cut-offs:

Probes -The boiler manufacturer will specify the point where they’d like to have this type of low water cut-off inserted. It will usually sit just below the water line, at a point above the boiler’s crown. A probe uses the boiler’s water to complete an electrical circuit past an insulator (the center portion of the

probe) back to a ground (the threaded portion of the probe). As long as water covers the probe, an electronic “go” signal will travel to the burner. When water drops off the probe for a continuous ten seconds, an electronic “stop” signal goes to the burner, shutting it down and protecting the boiler from a low water condition.

At ITT McDonnell & Miller, we manufacture several different types of probe low water cut-offs to meet any of your job applications.

One of those applications might involve the boiler’s water level. The water capacity of today’s boilers is considerably less than that of boilers from decades ago. Along with this, the water level operating range of today’s boilers is smaller. Further, the amplitude of surging water levels is increasing. As a result, the low water cut-off must be “smart” enough to recognize these variations and react appropriately. We have done this by incorporating delay features in the probe’s operating logic. These include a delay on break feature (DOB) which keeps the burner lit for 10 seconds after water leaves the probe. This minimizes the effects of a surging water line. Another addition - the delay on make feature (DOM) - allows an additional feed time of 15 seconds once water comes in contact with the probe. This minimizes rapid burner and feeder cycling by slightly elevating the water level so that water lost to steaming will return (in the form of condensate) before the water level drops below the probe.

Float Type - in operation, these are similar to the external, float operated low water cut-offs we looked at before. The difference is that instead of sensing a duplicated water level outside the boiler, these units sense the level directly inside


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the boiler. We make them for you in five mounting-barrel sizes (Series 69) to accommodate different boiler insulation thick-nesses. When you select a built-in float type control, make sure it fits as far as possible into the boiler without the float shield coming in contact with the boiler.

When a low water cut-off stops a burner, it also stops the entire heating system. Nothing will happen until the water in the boiler returns to a safe operating level.

While this is very good for the boiler, it may not be the best thing for the system. If the heat in the building is off for too long a time, water pipes may begin to freeze.

This is where automatic water feeders come in. An automatic feeder will maintain a safe minimum water level in the boiler and keep it operating, even if the system is leaking. It keeps the system operating automatically until you can make the repairs.

Hot Water Boilers

Low water protection isn’t just for steam boilers. Hot water boilers face the same perils of overheating damage if the water line drops too low. Many people don’t think of this as often as they should because hot water boilers serve “closed” systems. They have pressure-reducing valves that are sup-posed to feed water automatically should a leak develop.

The truth, however, is that a pressure reducing valve is no substitute for a low water cut-off. Pressure reducing, or “feed” valves, often clog with sediment and wind up not feeding at all. A buried pipe can corrode and spring a leak that flows faster than a “feed” valve can satisfy. Relief valves can pop and, while dumping water at a great rate, actually prevent the feed valve from operating.

Let’s take a closer look at how we can protect these boil-ers.

Hot Water Systems

As we said, the things that affect steam boilers also affect hot water boilers. If you run them with too much water, the

relief valve will open. If you run them with too little water, they’ll overheat and suffer damage.

A low water cut-off is the only sure way of protecting a hot water boiler from sudden loss of water. The ASME boiler code recognizes this by requiring all hot water boilers of 400,000 BTU/HR or more input to have low water fuel cut-off devices.

ASME doesn’t call for low water cut-offs on smaller, residen-tial boilers, but we think all hot water boilers, regardless of their size, must have protection. However, the International Mechanical Code requires low water cut offs on ALL hot water and steam boilers. ITT McDonnell & Miller make several devices, both float and probe type, that protect and meet


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the needs of any boiler whether it’s cast iron, steel, or cop-per construction.

Hot water systems regularly lose water through faulty air vents, loose valve stem packing, cracked boiler sections, loose nipples, corroded pipes, broken or loose pump seals, leaking gaskets, or dripping relief valves, to name just a few places. Most installers depend on their pressure reducing or feed valve to replace the lost water automatically. But feed valves often clog with sediment, especially in hard water areas. And it’s very easy to close the supply valve to a feed valve and forget to open it again.

On systems with buried pipes (say a radiant heating system) a feed valve will open if a pipe breaks. It will feed fresh water continuously until it either clogs (and stops feeding) or destroys the ferrous components of the system with oxygen corrosion. A simple feed valve can wind up costing a lot more than its purchase price. This is why major suppliers of feed valves, such as ITT Bell & Gossett, recommend you close the feed valve once you’ve established your initial fill pressure. This is also why we strongly recommend you use a low water cut-off on every hot water boiler. Feed valves are not a sub-stitute for low water cut-offs. They can’t protect your boilers from a low water condition. Feed valves are fine for filling the system initially, and for helping you vent air from the radiators, but once the system is up and running, you shouldn’t look to them for protection.

Over firing

There are times when hot water boilers don’t lock-out on safety. Whether by control failure or human error, things go wrong. And when they go wrong in a hot water heating system, the water temperature can rise quickly to a point where the compression tank can’t take up the expansion of the water. This causes the relief valve to discharge.

When the relief valve opens, there’s a sudden drop in system pressure. The water, which at this point is probably much hotter than 212°F (100°C), will flash into steam. This is why ASME insists that relief valves for hot water boilers carry steam-discharge ratings. If a feed valve doesn’t open to replace this rapidly exiting water, a low water condition will quickly result. The only thing that can protect the boiler at this point is a low water cut-off. The feed valve can’t protect the boiler because its typical setting is 12 psig (.83 bar). In


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other words, the system pressure must drop below 12 psig (.83 bar) before the feed valve will open.

The trouble is that while the relief valve is open and flashing steam to atmosphere, the internal system pressure never drops anywhere near 12 psig (.83 bar). A relief valve with a 30 psig (2.1 bar) setting, for instance, will open at 30 psig (2.1 bar) and close again when the pressure drops to about 26 psig (1.79 bar). The result is a loss of water with no make-up. Repeat this cycle enough times and the boiler will be in a dangerous low water condition. Keep in mind, steam exerts pressure. It can easily fool a feed valve, and that’s why feed valves offer very little protection at all against low water.

Feeder/Cut-Off Combinations for Cast Iron and Steel Hot Water Boilers

To protect a boiler from dry firing, the low water cut-off must be located above the boiler’s crown. After the low water cut-off shuts off the burner, you should have a way to add water to the system to ensure the crown stays under water.

A combination water feeder and low water cut-off can do this for you. If you position the feeder above the boiler’s crown, it will mechanically feed water if the level should drop to that point. This is an important consideration because even if the electricity is cut off, it’s possible for the firing cycle to continue if the fuel feed valve is mechanically locked open. The combination unit’s cut-off switch will act as a back-up to the primary low water cut -off, providing the boiler with ad-ditional protection.

Protecting Copper Fin Tube Boilers

Copper fin tube boilers move heat from the flame to the water almost instantly. This type of boiler depends on the proper flow of water across its heat exchanger to move the heat quickly out of the boiler and into the system. Should flow stop while the burner is operating, heat will quickly build and cause the water in the heat exchanger to flash into steam. This condition is similar to a dry firing in a cast iron or steel boiler. A McDonnell & Miller flow switch, installed on the copper fin tube boiler’s hot water outlet, protects it from this danger. The burner cannot fire unless water is moving across the flow switch. When the flow stops for whatever reason, the McDon-nell & Miller flow switch immediately cuts electrical power to the burner and protects the boiler from overheating.

Pressure Relief Valves

Good engineering practice calls for every hot water boiler to have a pressure relief valve. This spring loaded valve must


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be able to release the boiler’s entire load at the boiler’s maximum operating pressure. Here are some things that can cause a relief valve to open in a hot water heating system: • The automatic feed valve fails, allowing higher than normal pressure to enter the system.

• Someone leaves a hand bypass line open after filling the system.

• Someone hydrostatically tests the system at a pressure greater than the relief valve’s setting.

• The air cushion in the diaphragm type compression tank doesn’t match the system’s static fill pressure. Keep in mind most tanks come from the factory precharged at 12 psig (.83 bar). If the system needs more than 12 psig (.83 bar) pressure, you have to add more air to the tank, and you have to do this while you have the tank disconnected from the system.

• The compression tank may be too small for the system.

• The boiler’s aquastat is in a well without heat transfer grease. When this happens, the boiler’s temperature will quickly exceed the aquastat’s setting, causing rapid rise in system pressure.

• The circulator may be on the return side of the system with the compression tank at its suction. If it is, the circulator’s head pressure will appear inside the boiler as a net increase. It may be enough to open the relief valve.

• The burner limit may be jumped‑out or stuck in a manual position.

The main thing to keep in mind when you’re troubleshooting this one is that relief valves pop when any of these three things happen:

• The compression tank loses its air cushion• The system takes on more water.• The system temperature increases.

Think methodically, and keep your eyes wide open!

We hope this Basic System Operation Guide has given you insight into the systems on which you’re now working or will face in the future. We welcome any questions or comments you may have about the Guide, or about our products.

Thanks for your support, and for your continuing business.

tech tip #1 - federal corporation you end up doing is making your boiler and piping system a...

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